6-Alkyl- and aryl-4-amino-3-methylthio-1,2,4-triazin-5(4H)-ones are known (Dornow, Chem. Ber. 1964, 2173; U.S. Pat. Nos. 3,671,523; 3,961,936; 3,966,715; and 4,113,767) and one member of the class; i.e., the 6-tert.-butyl compound, is the widely used herbicide, metribuzin (Merck Index No. 6027). A variety of substituted types are known which possess herbicidal activity. 6-Carboxy and 6-(.delta.-carboxyalkyl)-3-mercapto-4-amino-1,2,4-triazin-5(4H)-ones are described in my copending application Ser. No. 06/238,480 filed 02/26/81. These 6-carboxyalkyl types are advantageously obtained from .alpha.-keto dicarboxylic acids thus avoiding the costly economic and environmental problems encountered in the manufacture of the 6-tert.-butyl derivative, metribuzin. These problems have been stated in detail in U.S. Pat. No. 4,113,767, which describes a sulfur dichloride chlorination process for the preparation of trimethylpyruvic acid, the primary starting material - a process which is a source of contaminating possibilities such as the chlorinated by-products resulting from sulfur dichloride chlorination of the tert.-butyl group. .alpha.-Ketoglutaric acid, the starting material for the preparation of the 6-(2'-carboxyethyl)-triazinone of the present invention is available from environmentally acceptable and economically advantageous fermentation processes (U.S. Pat. Nos. 2,443,919; 2,841,616).
3-Methylthio-triazin-5(4H)-ones have been previously and customarily prepared by reaction of a strongly alkaline solution of the 6-mercaptotriazinone with methyl iodide (U.S. Pat. Nos. 4,113,767; 4,036,622). There is no known previous reference to the use of S-methylthiocarbonohydrazide iodide, the preparation which is given in J. Org. Chem. 19, 1231 (1954), for the preparation of 3-methylthio-4-amino-6-substituted-1,2,4-triazin-5(4H)-ones of any type.